Scientists are seeking new ways to reverse the buildup of carbon dioxide in the atmosphere that many believe is the cause of global warming. Today on Searching for Solutions, VOA's Brian Wagner reports that one project in the United States aimed at stimulating plankton growth in the oceans is raising some debate about its possible effectiveness.

Dumping tons of iron dust into the ocean may not appear to benefit the environment. But researchers with the U.S. firm Planktos say it is crucial to their efforts to stimulate plankton growth and remove carbon dioxide from the atmosphere.

Melodie Grubbs, a climate expert with the firm says, "Once we put that in, iron acts as a catalyst for photosynthesis, which creates plankton. It's a missing nutrient in the ocean and from that sparks a natural plankton bloom."

Researchers say plankton organisms are struggling because less iron dust is being blown onto the ocean's surface by nutrient-rich winds. The Planktos team hopes to reverse the trend by seeding the waters off the Galapagos Islands and several other spots in the Pacific Ocean with a special form of iron dust.

"So we'll combine this with sea water first, concentrate it, then put it back in the ocean, and then do a zig-zag pattern to get the best coverage we can" says Grubbs describing the technique.

Like trees, plankton absorbs carbon dioxide and converts it into biomass, which can remain under water for centuries. Critics of the Planktos model, however, say it is nearly impossible to prove how much carbon dioxide is pulled from the atmosphere.

Frank Millero is a professor of marine chemistry at the University of Miami. He helped pioneer research into iron fertilization in the 1990s. "The problem, if there is one, is if the carbon dioxide in the plant material does not sink to the deep waters and become oxidized there, then the net effect is not as large as you might hope for."

Millero says the team will have to continue dumping iron to trigger new plankton blooms, and he says that will be very costly.

To support its efforts, Planktos hopes to get financing from major companies as a way to offset the greenhouse gases released through manufacturing or other activities.

The firm's Pacific project manager Michael Bailey says these carbon credits are generating new opportunities in environmental restoration. "We are part of the international carbon credit community, part of that marketing plan, basically trying to find a way to make money by restoring the ocean's and the earth's atmosphere. So this is a beautiful business model."

Environmental experts may not agree on the best way to reverse decades of carbon dioxide emissions, but they do agree that more efforts are needed to remove the gas from the atmosphere.